package twoways;

public class TailRecursionToIteration {
    
    ProblemSpecAndTools psat;
    
    public TailRecursionToIteration(ProblemSpecAndTools psat) {
        this.psat = psat; 
    }
    
    public Object findRecursively() {
        if (psat.isBaseCase()) {
            psat.updateAccumulatorBaseCase();
            return psat.accumulator();
        }
        else {
            psat.updateAccumulatorNonBaseCase();
            psat.reduceProblem();
            return findRecursively();
        }
    }
    
    public Object findIteratively() {

        ///////////////////
        // ADD CODE HERE //
        ///////////////////

    }
    
    public static class FactorialPSAT implements ProblemSpecAndTools{
        private int n;
        private int a; //accumulator
        
        public FactorialPSAT(int n) {
            this.n = n;
            this.a = 1;
        }
            
        public boolean isBaseCase() {
            return n == 0;
        }

        public void reduceProblem() {
            n--;
        }
                
        public void updateAccumulatorBaseCase() {
            // do nothing
        }
            
        public void updateAccumulatorNonBaseCase() {
            a = n * a;
        }
            
        public String toString() {
            return "" + a;
        }

        public Object accumulator() {
            return a;
        }
    }
    
    public static class StringReverserPSAT implements ProblemSpecAndTools {
        
        ///////////////////
        // ADD CODE HERE //
        ///////////////////
    }
    
    public static class GcdPSAT implements ProblemSpecAndTools {
        
        ///////////////////
        // ADD CODE HERE //
        ///////////////////
    }
}